Burglar-proof lock



June 10, 1969 A. PETRI 3,449,006

BURGLAR- PROOF LOCK Filed 001;. 23, 1967 I NVEN TOR. ANDREW PETR/ ATTORNEY United States Patent 3,449,006 BURGLAR-PROOF LOCK Andrew Petri, 1787 Lombard St., San Francisco, Calif. 94123 Filed Oct. 23, 1967, Ser. No. 677,339 Int. Cl. E05b 15/12, 15/02 US. Cl. 292346 3 Claims ABSTRACT OF THE DISCLOSURE The commonly-used Schlage-type lock is modified to improve its resistance to burglary. A secondary bolt is installed in the jamb of the door, such bolt being springbiased outward and provided with a dead-latch plunger which prevents retraction of the secondary bolt when the plunger is retracted. The primary bolt on the door is fixed in projected position so that it can only be retracted by turning the door knob on the inside of the doorway or the key on the outside. The primary bolt has a projection which is positioned to engage the dead-latch plunger of the secondary bolt when the door is closed. The two bolts are formed with complementary flats so that the bolts interfit when the door is closed. When a burglar attempts to force the primary bolt inwardly with a blade inserted between the door stop and door, the force is resisted by both bolts. Since the housing of the secondary bolt is recessed relatively deeply into the jamb, the jamb does not rupture readily.

This invention relates to a new and improved burglar resistant lock construction. Conventional locks employ primary bolts in the door which fit into a bolt receiving recess in the jamb. Usually, the opening in the jamb is surrounded by an apertured striker plate held in position with two wood screws and sometimes the structure is reinforced by a bolt-receiving sheetmetal box which lines the hole in the jamb and is either attached to the striker plate or has flanges which underlie the underside of the striker plate.

In burglarizing such locks, a blade is inserted between the door and the door stop and forced against the primary bolt or a strong force is applied to the door itself adjacent the location of the primary bolt. Such forces tend to rip the bolt inwardly, fracturing the wood of the jamb around the bolt receiving hole. The screws holding the striker plate in place are torn out and the metal lining of the hole does not effectively resist such force. Experience has shown that this is one of the most common methods of gaining illegal access through a locked door of this general type. The present invention is designed to deter such access. This is accomplished by means of a secondary bolt which is recessed relatively deeply into the jamb. Accordingly, the depth of the secondary bolt requires a much greater force in order to fracture the structure of the jamb around the lock bolts and thus prevents illegal entry.

Another feature of the invention is the fact that the primary bolt in the door fits more deeply into the hole in the jamb, the striker plate and surrounding mechanism being grooved to receive the outer end of the primary bolt in order to effect the interfitting of the two bolts as hereinafter explained.

A still further feature of the invention is the fact that the primary bolt in the door is held in projected position at all times except when the door handle or door key are turned to retract the primary bolt. In effect, therefore, the primary bolt is at all times dead-latched.

Still another feature of the invention is the fact that the secondary bolt in the jamb is also provided with a dead-latch feature which is automatically engaged by a 3,449,006 Patented June 10, 1969 projection carried by the primary bolt. Thus, when the door is completely closed, both the primary and the secondary bolts are dead-latched. This feature of the invention prevents another means of gaining illegal access to premises by inserting a flexible strip behind the bolt to retract the same or engaging the side of the bolt with a sharp blade and gradually working the bolt into retracted position by manipulation of the blade.

A still further feature of the invention is the fact that both the primary and the secondary bolts are cut away in flat surfaces which mate so that the two bolts fit close together with broad parallel faces. Such relationship for practical purposes prevents entry of a flexible strip between the two bolts.

A still further feature of the invention is the fact that the primary and secondary bolts can be installed in existing door structures with a minimum of labor merely by boring a deeper hole in the jamb to receive the housing of the secondary bolt and by replacing the standard primary bolt in the door with a special primary bolt as hereinafter described. Accordingly, the present invention requires little change in the lock structure and the installation is inexpensive in labor and also in the cost of the parts employed.

Other objects of the present invention will become apparent upon reading the following specification and referring to the accompanying drawings in which similar characters of reference represent corresponding parts in each of the several views.

In the drawings:

FIG. 1 is a perspective view of a portion of a door and jamb showing the parts of the present invention with the door open.

FIG. 2 is a horizontal sectional view through the lock structure with the door in closed position.

FIG. 3 is a view similar to FIG. 2 showing the door and jamb in exploded position.

As shown in the accompanying drawings, a door 11 is hinged to a door frame (not shown) located to the right of FIGS. 1-3, inclusive. The inside of the doorway is indicated by the letter I and the outside of the letter O in FIGS. 2 and 3. Opposite the free edge of door 11 is a jamb 12 and at the outside it is provided with a stop 13 which limits swinging movement of the door beyond normal closed position.

Installed in door 11 is a lock structure 14 of the common commercially available Schlage-type, it 'being understood that the invention is useful with other locks. How ever, in view of the well-known structure of such locks, it is believed unnecessary to illustrate or describe in detail the bolt retracting mechanisms since such mechanisms are relatively unchanged in the present invention. Accordingly, on the inside of the door is a handle 16 and on the outside a second handle 17. Key 18 on the outside is used to open the lock from the outside, whereas the handle 16 may be used to open it from the inside. Mounted in the free edge 19 of the door 11 is a primary bolt casing 21 which is circular in cross section and which engages the lock structure 14. The casing 21 is held in place by an apertured plate 22 recessed into the edge 19 and held in position 'by screws 23. Projecting through the aperture in plate 22 is a bolt 26 which is normally spring biased outwardly, its retraction being controlled by the lock 14 when either the handle 16 or the 'key 18 is turned. The shape of bolt 26 is modified from the conventional shape in that a notch is cut into the bolt so that there is a vertical, substantially medial surface 27 parallel to the face of the door 11 and a vertical transverse surface 28. The surfaces 27 and 28 intersect at approximately right angles and the surface 28 is approximately flush with the outside face of the plate 22. The bolt 26 is further modified by a projection 29 on its outside face for a purpose which hereinafter appears. Bolts of this general type are frequently provided with a dead-latch feature wherein a plunger 31 is positioned adjacent the bolt 26. When such plunger 31 is retracted by contact with a surface of the door jamb, mechanism forming no part of this invention but well understood in the art lock prevents retraction of bolt 26 against the force of the spring except either by turning the knob 16 or the key 18. In other words, when the plunger 31 is retracted, no external force can retract bolt 26. In accordance with the present invention, the plunger 31 is permanently retracted so that the primary latch 26 is always projected except when the knob or key are turned. It will be readily understood that rather than using the plunger 31 for dead-latching purposes, other mechanisms may be employed to accomplish the same result.

The foregoing structure is essentially the standard lock structure except for the cutout surfaces 27, 28 of the bolt 26, the projection 29 and the permanent dead-latching of the plunger 31.

Jamb 12 is formed with a circular hole 36 of relatively great depth immediately opposite primary bolt 26 and fitting within the hole 36 is a secondary bolt casing 37 which is substantially circular in cross section. Casing 37 is held in place by striker plate 38 which has an outturned guide surface 39 as well understood in this art. However, the guide surface 39 and the plate 38 are formed with a groove 40 to provide clearance for the bolt 26 and projection 29 when the door closes, it being understood that the bolt 26 is usually projected. Plate 38 is held in place by screws 45. It is important to note, however, that the screws are not the primary instrumentality holding the structure in position and more particularly that the casing 37 is recessed deep within the jamb 12.

Projecting outward of casing 37 is secondary bolt 41 which extends beyond the plane of plate 38. The inside edge of bolt 41 is rounded as indicated by reference numeral 42. Hence, when bolt 26 (or projection 29) engages the rounded surface 42, bolt 41 is retracted against the force of the spring (not shown) which normally projects the 'bolt until the primary bolt 26 has passed secondary bolt 41. Secondary bolt 41 is formed with a notch complementary to the notch in the primary bolt. Thus, there is a vertical substantially medial surface 43 parallel to the plane of door 11 and a transverse outward extending surface 46 (see FIG. 1) which is recessed slightly inside plate 38. It will be noted that the projecting portion of primary bolt 26 is outside vertical face 27 whereas the projecting portion of secondary bolt 41 is inside the surface 43. Secondarybolt 41 is also provided with a deadlatch plunger 44 which is positioned opposite projection 29 in the closed position of the door. Hence, when the door closes, dead-latch 44 is retracted which prevents retraction of bolt 41 against the force of the spring in the casing 37 so long as door 11 remains closed.

In normal operation of the door latch mechanism, as the door 11 is closed, projection 29 engages striker flange 39 and fits into groove 40. The projection engages the rounded surface 42 of bolt 41 forcing the same closed. Thereupon, projection 29 engages secondary plunger 44. The latches 26 and 41 interfit in that surfaces 27 and 43 are in close proximity and parallel to each other in the closed position of the door as is best shown in FIG. 2. Furthermore, projection 29 dead-latches the plunger 44 preventing retraction of bolt 41. When it is desired to open the door, either the knob 16 or the key 18 is turned, which retracts plunger 26 permitting the door to open 4 and the parts to return to their projected position as viewed in FIG. 3.

As best shown in FIG. 2, when the door is closed it is substantially burglar proof. There are two bolts, 26 and 41, in position in the gap between the door and the jamb. Both of these bolts are dead-latched in projected position. Because of the close interfit of surfaces 27 and 43, entry of a prying tool from above or below the location of the lock is prevented. Secondly, the entry of a flexible strip of celluloid or other material between the door 11 and the stop 13 into the gap between the door and jamb is futile because both bolts 26 and 41 are dead-latched and cannot be cammed to retracted position. Thirdly, and most importantly, if a strong force is applied from the outside against door 11 or bolt 26 tending to drive the same inward, such force is resisted by bolt 41 which extends into casing 37 which in turn extends deep in the hole 36 in jamb 12. Hence, all of the material of the jamb 12 around the hole 36 resists rupture or fracture, a common cause of failure of locks in standard installations.

Accordingly, the present invention provides what is essentially a burglar-proof installation.

What is claimed is:

1. In a double lock construction, a primary bolt adapted for mounting in a door for reciprocation longitudinally of said bolt, resilient means biasing said bolt into projected position projecting beyond an edge of said door, manually operable means for retracting said primary bolt, a secondary bolt, a housing for said secondary bolt, of extended length, said housing adapted for installation in a hole in a door jamb which, when said door is closed, is in registry with said primary bolt, means in said housing for biasing said secondary bolt outwardly of said housing to projected position, retaining means retaining said housing in said jamb, the inner side of the outer end of said primary bolt formed with a first notch and the outer side of the outer end of said secondary bolt formed with a second notch whereby in closed position of said door the outer end of said primary bolt overlaps and lies outside of and in close proximity to the outer end of said secondary bolt.

2. A lock construction according to claim 1 in which said primary bolt is permanently deadlocked in projected position and resists inward movement resulting from all forces applied in an inward direction to the outer end of said primary bolt, said retaining means and said housing recessed to provide clearance for said primary bolt as said door approaches closed position.

3. A lock construction according to claim 1 which further comprises a deadlock plunger reciprocable in said housing on the outer side of said secondary bolt, said deadlock plunger when retracted holding said secondary bolt against retraction, said primary bolt formed with a projection to retract said deadlock plunger when said door is closed.

References Cited UNITED STATES PATENTS MARVIN A. CHAMPION, Primary Examiner.

EDWARD J. MCCARTHY, Assistant Examiner.

U.S. Cl. X.R. 292341.15 

